And if Joe Bloggs complains, 'Hey, that wasn't me! Leave my good name alone!' and Wikipaedia refuses to take it down and drags Joe Bloggs's name through the dirt even more while talking about it? Then Wikipaedia could probably get sued in the UK for failing to be an innocent disseminater. (See Defamation Act 1996, Laurence Godfrey v. Demon Internet Limited) Now, if Wikipaedia does take it down immediately (I don't trust it to, but if it did), Wikipaedia would proably be immune under the innocent dissemination clause, although whoever put the notice up might not be (but then again, who wants to sue Jane Admin anyway?). Of course, the entire incident could be avoided if everyone used pseudonyms that were obviously pseudonyms. Not that shaming a pseudonym is a good thing to do, but at least people are less likely to lose jobs over that.
A name is not a unique identifier. I don't see how anyone could claim something is defamation when it's not even about them.